Field of the Invention
The present invention relates to a method for generating a combined projection image (SM) from a medical inspection object and an imaging device for generating a combined projection image (SM) from a medical inspection object.
Computed tomography (CT), usually X-ray computed tomography, is a widely-used medical diagnostic tool, which allows the generation of tomographic images or slices of an area of interest in a patient. Radiologists often prefer using thick slab or thick-slice volume for diagnostic and screening reading. For example, 5.0 mm slabs are often used for clinical reading and data storage in thoracic CT, although thin, high resolution 0.5 mm slabs are available and used for computer applications such as three-dimensional volume rendering and computer aided diagnosis algorithms.
It is relatively easy to compute 3.0-5.0 mm slabs in thoracic CT images without losing diagnostically relevant information, for example by applying methods such as Average Intensity Projection (AIP) or Maximum Intensity Projection (MIP). The slab thickness is related to the combined thickness of the original slices in the volume. Generally, a slab is rendered as a two-dimensional image, so that the image can be printed or viewed on a computer screen.
In Digital Breast Tomosynthesis (DBT) data volumes are often reconstructed at a higher resolution, for example at a resolution of 85 microns for a slice thickness of 1.0 mm. Such a high-resolution volume allows visualization of the fine clinical details required for accurate medical diagnosis of breast cancer, for example microcalcifications of only 100 microns in size, very fine spiculations of masses, etc. A correct depiction of microcalcification morphology and spiculations is critical for the radiologist in order to be able to differentiate between benign and malignant lesions in breast tissue. This means that the amount of data in DBT volumes is very large. For example, the total volume of data for a single patient (e.g. including two DBT views and projection images) can exceed one gigabyte. The large data volume complicates data transfer and increases radiologist workload.
Another reason for generating slabs from the initial data is that a radiologist often needs to evaluate the distribution of an entire cluster of calcifications embedded in the surrounding tissue, including any masses and architectural distortions in that region.
In breast tissue, a lesion can often extend over 10.0 mm or more, and can extend in any random direction. Therefore, in order to be able to perform such an evaluation, a radiologist should be provided with very thick slabs, i.e. slabs with a thickness in excess of 10.0 mm. In some cases, it might be desirable to perform such an evaluation over the total volume (essentially the whole volume collapsed into a single slab). In the context of DBT such a single slab has also been called synthetic mammogram (SM) due to its similarity to conventional 2D mammograms.